利用球形压头研究聚碳酸酯的微米划痕性能

Microscratch Properties of Polycarbonate by Spherical Indenter

采用100Cr6球形压头系统研究了法向载荷、划痕速度和划痕次数对聚碳酸酯划痕性能的影响.结果表明:在单次和第15次划痕中,法向载荷增加时,摩擦系数和压入深度增加;划痕速度增加时,摩擦系数先增加后减小,压入深度减小;法向载荷增加或划痕速度减小时,残余深度增加,弹性恢复率减小.对于多程单向滑动磨损,随着划痕次数增加,划痕宽度线性增加,划痕硬度线性减小;摩擦系数、压入深度和残余深度均呈增加趋势,但增长的速率逐渐降低,一定次数后达到稳定;压入深度和残余深度达到稳定时的划痕次数随法向载荷的增加而减小.第15次划痕中,随着法向载荷增加,划痕宽度增加,残余划痕硬度和几何划痕硬度变化趋势相反;划痕宽度随划痕速度的增加而减小,划痕硬度随划痕速度的增加而增加,最后均趋于稳定.

The effects of normal load,scratch speed and the number of scratches on the scratch performance of polycarbonate were studied by using 100Cr6 spherical indenter.The results showed that in the single scratch,the friction coefficient and the sum of adhesion and viscoelastic friction coefficients increased nonlinearly;penetration depth and ploughing friction coefficient increased linearly with the increase of normal load.In the 15 th scratch,the friction coefficient,penetration depth and ploughing friction coefficient increased linearly,the sum of adhesion and viscoelastic friction coefficients decreased linearly with the increase of normal load.In the single scratch and the 15 th scratch,the friction coefficient,the sum of adhesion and viscoelastic friction coefficient increased first and then decreased with the penetration depth,and ploughing friction coefficient decreased linearly as the scratch speed increases.In addition,with the normal load increasing or scratch velocity decreasing,the residual depth increased and the elastic recovery rate decreased.The Knoop hardness decreased with the increase of normal load,which indicated the indentation size effect in polycarbonate.For multi-pass unidirectional sliding wear test,with the increase of the number of scratches,the scratch width increased linearly,and the scratch hardness decreased linearly.Moreover,the friction coefficient,penetration depth and residual depth increased with a power law dependence on the number of scratches.In the process of multiple scratches,a hardening layer around the scratch groove formed,and the hardening layer after each scratch became more compacted.As a result,the growth rates of friction coefficient,penetration depth and residual depth gradually decreased and reached stable levels after a certain number of scratches.The numbers of stable scratches for penetration depth and residual depths decreased with the increase of normal load.In the 15 th scratch,under low normal loads and scratch speeds,the strain rate decreased with the increase of normal load or the decrease of scratch speed,which led to the deterioration of resistance to plastic deformation and the linear decrease of scratch hardness.Polycarbonate exhibited stress whitening,ironing and regular zig-zag type scratch tracks.The scratch morphology was severely damaged with both residual scratch width and geometric scratch width increasing linearly with the increase of normal load.The residual scratch hardness decreased with a power law dependence on the normal load,while the geometric scratch hardness increased due to work hardening and the increase of strain as the normal load increased.The damage extent of scratch surface decreased with the increase of scratch speed.The residual scratch width and geometric scratch width decreased linearly with the increase of scratch speed.In addition,the residual scratch hardness and geometric scratch hardness increased with the increase of scratch speed,and finally tended to be stable.The derivative of scratch hardness with respect to the square of strain rate was related to the scratch speed:as the scratch speed increased,the slope of the curve gradually decreased.As the scratch speed was large enough,it tended to be zero.Under low normal loads or high scratch speeds,the material was compressed and sunk in around the borderlines of the scratch groove,giving rise to the geometric scratch width greater than the residual scratch width.Nevertheless,for high normal loads or low scratch speeds,a small amount of material piled up on both sides of the scratch groove,resulting in a smaller geometric scratch width than the residual width.